Berlin 2005 – wissenschaftliches Programm
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DY: Dynamik und Statistische Physik
DY 24: Granular Matter
DY 24.5: Vortrag
Samstag, 5. März 2005, 15:15–15:30, TU H2032
Volume fluctuation measurements towards a granular statistical mechanics — •Matthias Schröter, Daniel Goldman, and Harry Swinney — Center for Nonlinear Dynamics, The University of Texas at Austin
Edwards and Oakeshott (Physica A 157, 1080 (1989)) proposed a statistical mechanics approach to static granular media based on the idea that each mechanically stable configuration of particles corresponds to a microstate of the system. We explore this granular phase space using flow pulses in a fluidized bed. This way of driving results in a steady state with a volume fraction φ which is controlled by the flow rate of the pulses. These steady states are shown to be history independent. φ exhibits Gaussian fluctuations with a standard deviation σφ which has has a parabolic minimum as a function of φ. Interpreting this result in terms of statistically independent regions leads to a better understanding of the geometrical properties of particle packings. The knowledge of σφ allows also to determine for the first time the compactivity X of a granular system. X is a temperature-like state variable introduced by Edwards and coworkers.